Phase shifters are used in systems to change a transmission phase angle of an input signal. Their most recognized application is in phased array antennas that include multiple transmitting and/or receiving antenna elements that can be used together to form a directional radiation pattern. The relative phases or the respective signals feeding the antennas are controlled using phase shifters to create an effective radiation pattern that is strongest in a desired direction and suppressed in undesired directions. In this manner the antenna beam may be rapidly steered without any mechanical steering of the antenna (e.g., using a gimbal).
Quantized or “digital” phase shifters may be used to control the phases of the signals feeding the antenna elements by providing a discrete number of phase states controlled using phase bits having two states, where for n-bit phase shifter there are 2n states available. As such, the higher the number of phase bits, the more accurate the phase shifter. For example, in the case of an ideal 2-bit phase shifter, the phases of the signals may switch between four states, 0°, 90°, 180°, and 270°, which have a step size of 90° and a maximum quantization error of ±45°. In the case of an ideal 3-bit phase shifter, the phases of the signals may switch between eight states, 0°, 45°, 90° 135°, 180°, 225°, 270°, and 315°, which have a step size of 45° and a maximum quantization error of ±22.5°.
In commercial practice, switched line phase shifters are typically used in digital phase shifters as fundamental components for phased array antennas. These phase shifters typically use PIN diodes (diodes having an undoped intrinsic semiconductor region between p-type and n-type semiconductor regions) for switching between different transmission lines. FIG. 1 illustrates a basic schematic of a conventional design of a 1-bit (two state) switched line phase shifter 10. In this design, two, Single Pole Double Throw (SDPT) switches, including four PIN diodes 11a-d, are used to route a signal flow between one of two transmission lines, L1 or L2, having a different electrical length (e.g., in wavelengths). For each transmission line, the phase may depend on the electrical length of the line and the propagation constant of the line. As such, a phase shift between the two lines is realized by differing the electrical lengths of the lines. In this implementation, a RF signal (e.g., a signal having a frequency between about 3 kHz to 300 GHz) may be routed through line L1 (and thus have a phase delay ϕ1 based on the length of L1) by forward biasing (turning “on”) PIN diodes 11a and 11b and applying no bias to or reverse biasing (turning “off”) PIN diodes 11c and 11d. Alternatively, a signal may be routed through line L2 (and thus have a phase delay ϕ2 depending on the length of L2) by turning on PIN diodes 11c and 11d and turning off PIN diodes 11a and 11b. In this implementation, each of the turned on PIN diodes is individually forward biased using a PIN diode bias circuit (not shown) that provides a controlled forward bias current (e.g., about 5-10 mA) for each pin diode.
FIG. 2 illustrates a basic schematic of a conventional design of a 3-bit switched line phase shifter 20. As illustrated, the circuit block of FIG. 1 is repeated three times, in series, to provide 3-bits (i.e., eight possible phase states). Phase shifter 20 requires twelve PIN diodes and six transmission lines.